Advances in technology for wireless communication devices, such as cellular telephones, enable characteristics, such as cost, size, weight, and power, of the devices to be reduced while maintaining or improving performance standards of the devices, thereby improving the portability of the devices to the point where the devices are now commonly used as a replacement for conventional landline telephones.
One effective approach to reducing the cost and size of wireless communication devices is to use the same component for more than one function of a device. This approach may be known as increasing component integration or circuit reuse.
While the advances have improved the portability of the devices, consumers of the devices continue to demand more functions and services for the devices. For example, manufacturers of the devices have developed devices that operate at two or more frequency bands (i.e., multiple bands), for example, two frequency bands, to permit the devices to operate within an environment having more than one communications network. For example, a cellular telephone that operates at two frequency bands may be referred to as a dual band cellular telephone.
One exemplary environment having more than one communications network is a cellular communications network operating according to standards known as Code Division Multiple Access (CDMA), operating in a frequency band having a carrier frequency around 850 MHz, and as Personal Communications System (PCS) operating in a frequency band having a carrier frequency around 1950 MHz. Another exemplary environment is a cellular communications network operating according to standards known as GSM (Global System for Mobile communications), operating in a frequency band having a carrier frequency around 900 MHz for Standard GSM, and as Digital Communications System (DCS) operating in a frequency band having a carrier frequency around 1800 MHz for DCS 1800. Various other examples of combinations of standards in communications networks, digital or analog, are known or possible.
A wireless communication device transmits and receives signals for communication to occur. A transmitter, either separate from or part of a transceiver, transmits the signals for the wireless communication device. A transmitter typically accepts baseband signals, internally generated by the device, for transmission. The baseband signal may be in the form of a digital signal, known as a complex signal, such as In-phase (I) and Quadrature-phase (Q) signals. Typically, a transmitter subsequently performs forms of digital-to-analog conversion, frequency modulation, and power amplification of the baseband signals.
A wireless communication device that operates in more than one frequency band needs to transmit signals in each frequency band, thereby requiring more than one transmit function. For example, this may require having more than one separate function for each function of digital-to-analog conversion, frequency modulation, and power amplification. In particular, for example, a dual band transmitter may be implemented with two separate transmit signal paths, one for a high frequency band transmitter (e.g. 1950 MHz) and another for a low frequency band transmitter (e.g. 850 MHz). However, two separate transmit signal paths increase the cost and size (e.g., integrated circuit die area) of the wireless communication device to support dual band capability.
Advances in technology of wireless communication devices enable the cost and size of a dual band transmitter to be reduced while maintaining or improving performance standards of the devices, as shown in FIGS. 1 and 2, for example. FIGS. 1 and 2 illustrate a block diagram representation of first 100 and second 200 dual band radio frequency (RF) transmitters, respectively, according to the prior art.
In FIG. 1, the dual band RF transmitter 100 includes a baseband filter 102, a voltage controlled oscillator (VCO) 108, a local oscillator (LO) buffer 110, two frequency dividers 112 (divide by 4) and 114 (divide by 2), two mixers 104 and 106, two RF variable gain amplifiers (VGA) 116 and 124, two transformers 118 and 126, two driver amplifiers (DA) 120 and 128, and two RF SAW filters 122 and 130. FIG. 1 describes the area in terms of width and length (w/L) needed on an integrated circuit die using a 180 nanometer CMOS semiconductor manufacturing process for each of the two mixers 104 and 106, the two RF VGAs 116 and 124, and the two DAs 120 and 128. The baseband filter 102, the VCO 108, the LO buffer 110, the frequency divider 112 (divide by 4), the mixer 104, the RF VGA 116, the transformer 118, the DA 120, and the RF SAW filter 122 provide elements for a first transmit path configured to generate transmit signals in the cellular frequency band, for example. The baseband filter 102, the VCO 108, the LO buffer 110, the frequency divider 114 (divide by 2), the mixer 106, the RF VGA 124, the transformer 126, the DA 128, and the RF SAW filter 130 provide elements for a second transmit path configured to generate transmit signals in the PCS frequency band, for example. The baseband filter 102, the VCO 108, and the LO buffer 110 are common to and reused for each of the first and second transmit paths, thereby reducing the integrated circuit die area and associated cost for these common elements.
In FIG. 2, the dual band RF transmitter 200 includes a baseband filter 102, a VCO 108, a LO buffer 110, two frequency dividers 112 (divide by 4) and 114 (divide by 2), a buffer 132, one mixer 104, one RF VGA 116, two transformers 118 and 126, two DAs 120 and 128, and two RF SAW filters 122 and 130. FIG. 2 describes the area in terms of width and length (w/L) needed on an integrated circuit die using a 180 nanometer CMOS process for each of the mixer 104, the RF VGA 116, and the two DAs 120 and 128. The baseband filter 102, the VCO 108, the LO buffer 110, the frequency divider 112 (divide by 4), the buffer 132, the mixer 104, the VGA 116, the transformer 118, the DA 120, and the RF SAW filter 122 provide elements for a first transmit path configured to generate transmit signals in the cellular frequency band, for example. The baseband filter 102, the VCO 108, the LO buffer 110, the frequency divider 114 (divide by 2), the buffer 132, the mixer 104, the VGA 116, the transformer 126, the DA 128, and the RF SAW filter 130 provide elements for a second transmit path configured to generate transmit signals in the PCS frequency band, for example. The baseband filter 102, the VCO 108, and the LO buffer 110, the buffer 132, the mixer 104, and the VGA 116 are common to and reused for each of the first and second transmit paths, thereby saving the integrated circuit die area and associated cost for these common elements. Therefore, the dual band transmitter 200 in FIG. 2 reduces the integrated circuit die area and associated cost needed for the mixer 106 and the VGA 124 used in the dual band transmitter 100 in FIG. 1 by adding a much smaller integrated circuit die area and associated cost for the buffer 132 than what was reduced.
Accordingly, it is desirable to continue to reduce the integrated circuit die area and associated cost needed for a dual band transmitter even more than what is described for the dual band transmitters 100 and 200, shown in FIGS. 1 and 2, respectively, while continuing to maintain or improve performance.